1. Field of the Invention
This invention relates to a window unit having an adapter sill member for use in combination with a pre-installed sill disposed in an opening in a building wall.
2. Prior Art
The type of exterior window units with which this invention is concerned provides a high degree of thermal insulation, airtightness, and sound insulation since the units are mounted on the outside of openings in building walls, in which openings other window units have been previously installed. The exterior window units of this kind have found extensive use because they can retain the pleasing appearance of the pre-installed window assemblies having paper screen sashes (known as "Shoji" in Japan). The frame sills of the exterior window units usually include a hollow body of generally rectangular cross section having an upper and a lower portion, and an inner vertical side portion interconnecting the upper and lower portions at their inner ends or edges and having a pair of upper and lower vertical fins formed integrally therewith and extending therefrom one upwardly and the other downwardly, to form a first or vertical mounting portion to be mated with and secured to the exterior vertical surface of the sill of the previously installed window assemblies by screws or other fastening means which pass through the lower vertical fin, the frame sill also including a horizontal flange formed integrally with and projecting inwardly from the upper vertical fin at its top end to form a second or horizontal mounting portion to be mated with and secured to the top horizontal surface of the sill by screws or other fastening means passing through the horizontal flange. When it is desired to install the exterior window units from inside the building walls, it is difficult to fix the first or vertical mounting portion to the exterior vertical surface of the sill because of difficult access to the screw-receiving holes formed through the lower vertical fin extending downwardly of the frame sill body.
It has frequently been desired to increase the height of the upper vertical fins to provide a better weather resistance. Where standard sills having a thickness of from 36 mm to 45 mm are employed, the first or vertical mounting portion having such an increased upper vertical fin can not be secured directly onto the exterior vertical surface of the sill because the screw-receiving holes formed through the lower vertical fin are located downwardly of the sill when the first or vertical mounting portion is mated with the exterior vertical surface of the sill. One method of overcoming this difficulty has been to interpose an additional wooden plate between the first or vertical mounting portion of the frame sill and the exterior vertical surface of the sill and to fix the first or vertical mounting portion to the exterior vertical surface of the sill by screws passing through the lower vertical fin and the wooden plate. This procedure has been found not entirely satisfactory, however, in that it increases the installation costs on account of the use of such added materials. Another alternative has been to provide screw-receiving holes through the lower vertical fin of the first or vertical mounting portion in alignment with the positions of studs in the wall and to fix the first or vertical mounting portion to the exterior vertical surface of the sill by screws passing through the screw-receiving holes into the studs. This approach is also disadvantageous in that it requires a relatively time-consuming operation to drill or otherwise process the lower vertical fin to provide such screw-receiving holes at the construction site because the locations of the studs in the walls are not always constant.